1. Field of the Invention
The present invention relates to an image reading apparatus for reading an image output from an image forming apparatus, such as an electrophotographic apparatus and a laser printer, and an image processing method for processing the image read by the image reading apparatus.
2. Description of the Related Art
In an image reading apparatus, a reference value for performing photoelectric conversion of a read object to image information is set in successively reading image information or at predetermined timing. In many cases, the image information (reference value) read over plural lines is averaged.
Jpn. Pat. Appln. KOKAI Publication No. 11-289432 discloses a method for determining a reference value using a statistical technique in averaging data obtained by reading white reference data of several lines. According to Jpn. Pat. Appln. KOKAI Publication No. 11-289432, it is described that the method can decrease influence of foreign matter adhering to a white reference plate.
In the method using the averaging or the method the statistical technique, when the foreign matter adhering to the white reference plate is small to a certain degree in performing detection and removal of the foreign matter and correction, large fluctuation is seldom provided to the white reference value. On the other hand, when the foreign matter adhering to the white reference plate is large such that the foreign matter exists across plural pixels, there is a problem that the white reference value becomes inaccurate.